In recent years, coal gasification techniques and gas purification techniques have been developed to effectively use coal as an energy medium. On the other hand, in the process of purifying gas generated by gasifying coal (gasified gas), a CO shift reaction expressed by the following expression (I) for converting CO included in gasified gas into CO2 is caused.CO+H2O→CO2+H2  (1)
In the CO shift reaction, a catalyst (a CO shift catalyst) is used to promote the reaction. However, because CO shift reactions are exothermal, the temperature in the shift reactor may increase to approximately 400° C. the durability of the CO shift catalyst may be reduced.
As measures for preventing the reduction in the durability of such a CO shift catalyst, the techniques disclosed in Patent Literatures 1 and 2 are known.